A complete window typically includes a glass unit and a window frame.
A glass unit typically includes a pair of glass panes and a spacer, wherein the pair of glass panes is separated and held in a spaced-apart parallel relationship by the spacer, thereby defining an interior space within the glass unit.
A glass unit may also include one or more intermediate layers within the interior space, between the pair of glass panes. The intermediate layers may be constructed of film, glass or some other suitable material. A purpose of the intermediate layers is to increase the thermal resistance of the glass unit. The thermal resistance of a glass unit generally increases with the number of intermediate layers which are included in the glass unit.
A glass unit is typically mounted within a window frame in order to provide a complete window, and a complete window is typically installed in a wall or opening in a building.
A glass unit may be a sealed glass unit or a pressure compensated (i.e., “open”) glass unit.
A sealed glass unit can prevent moisture from entering the interior space within the glass unit as long as the integrity of the seal or seals is maintained. The interior space of a sealed glass unit can also be filled with a gas which has a relatively high thermal resistance (such as argon, krypton or xenon) in order to further increase the thermal resistance of the glass unit. Unfortunately, the components of a sealed glass unit (such as the glass panes, intermediate layers, and seals) can be exposed to significant stresses due to temperature and pressure fluctuations which may occur within the interior space of the glass unit during the installation life of the glass unit.
A pressure compensated glass unit can mitigate the extent to which the components of the glass unit are exposed to stresses due to temperature and pressure fluctuations, but a pressure compensated glass unit can introduce moisture into the interior space of the glass unit because the interior space communicates with the exterior of the glass unit in order to transfer air between the interior space of the glass unit and the exterior of the glass unit, and because the air at the exterior of the glass unit invariably contains some amount of ambient moisture.
In both a sealed glass unit and a pressure compensated glass unit, a desiccant can be used to reduce the amount of moisture present within the interior space of the glass unit, in order to provide relatively dry gas within the interior space.
In a sealed glass unit, the desiccant may be contained within one or more desiccant chambers which are in fluid communication with the interior space of the glass unit, so that residual moisture can be removed from the gas which is sealed within the interior space of the glass unit.
In a pressure compensated glass unit, the desiccant may be contained within one or more desiccant chambers which are in fluid communication with both the interior space of the glass unit and the exterior of the glass unit, so that air which is transferred from the exterior of the glass unit to the interior space is stripped of moisture before entering the interior space.
The one or more desiccant chambers may be incorporated into the spacer of the glass unit, and/or may be external to the glass unit. A disadvantage of using a desiccant in a glass unit is that the desiccant becomes saturated or spent as it absorbs and/or adsorbs moisture. As a result, the installation life of a glass unit which includes a desiccant may be dependent upon the service life of the desiccant, or the glass unit must facilitate the replacement of the desiccant at the end of its service life.
Examples in the prior art of sealed glass units and pressure compensated glass units which address the reduction of moisture within the interior space and which may also address the thermal resistance of the glass unit include U.S. Pat. No. 4,334,398 (Grether), U.S. Pat. No. 4,563,843 (Grether), U.S. Pat. No. 5,237,787 (Grether et al), U.S. Pat. No. 5,260,112 (Grether et al), U.S. Pat. No. 7,571,583 (Winfield), Canadian Patent No. 2,507,108 (Winfield), and Canadian Patent Application No. 2,551,356 (Clarahan).
There remains a need for a pressure compensated glass unit which can provide relatively dry air within the interior space of the glass unit and which can be adapted to provide a desired amount of thermal resistance of the glass unit.